1. Field of the Invention
The present invention relates to a method for producing a clad plate, more particularly a metal-clad plate, such as a titanium- or stainless-steel-clad plate, by means of rolling. The present invention is particularly characterized by the bonding in the rolling method for producing the metal-clad plate and by the process for assembly of a blank of a metal-clad plate.
2. Description of the Prior Art
It is difficult to produce titanium-clad plates and other metal-clad plates by means of rolling. Therefore, metal-clad plates are mainly produced by the explosive welding method. The explosive welding method, however, has numerous inherent limitations, such as the inability to process large-sized workpieces and the limited quality of the product.
It is known from Japanese Unexamined patent publication (Kokai) No. 52-13460 to apply copper plating to at least one of the surfaces of cladding titanium and a steel base, evacuate all gas from the space between the cladding titanium and steel base, then roll the cladding titanium and steel base. Assuming the workpiece to be rolled is subjected to a constant rolling force from one end to the other, this method of rolling may be classified as a conventional hot-rolling method.
When a conventional hot-rolling method is employed for producing clad plates, the cladding assembly sometimes breaks during the rolling, not only scattering fragments and bending and abnormally deforming the workpiece, but also, especially in the case of a titanium-clad plate, allowing oxidation of the predetermined bonding surfaces and intrusion of foreign matter onto the predetermined bonding surface, thereby reducing the field of the clad plate.
In a cladding assembly disclosed in Japanese Unexamined Patent Publication No. 52-13460, a cladding titanium sheet is welded to a steel base via distant pieces. This structure, however, is not completely satisfactory for preventing the reduction in yield during the hot-rolling.
On another matter, when a clad plate is produced by a conventional rolling method, the material having the lower deformation resistance is forced to flow toward the rear end as seen in the rolling direction. This causes significant deviation of the clad ratio, i.e., the ratio of thickness of cladding metal to the thickness of the base, from the target value and variation of the same in the rolling direction. It also results in a large cropping amount at the ends of the clad plate. These problems are particularly serious when titanium-clad plates are produced by rolling with a high reduction ratio. In addition, these problems are not eliminated by the methods of the above described Japanese unexamined patent publications.